The present invention relates to methods and compositions for increasing the viscosity of a fluid. More particularly, the present invention relates to multifunctional boronic crosslinkers, viscosified treatment fluids, and methods of using these compositions in applications wherein viscosified fluids may be used.
Many industrial applications require viscosified fluids or “viscosified treatment fluids.” As used herein, the term “treatment,” or “treating,” refers to any subterranean operation that uses a fluid in conjunction with a desired function and/or for a desired purpose. The terms “treatment,” and “treating,” as used herein, do not imply any particular action by the fluid or any particular component thereof. For instance, the upstream energy industry uses viscosified treatment fluids in a variety of production and stimulation operations. For example, such fluids may be used as drilling fluids, fracturing fluids, and gravel packing fluids. Generally, the viscosified treatment fluids that are used in subterranean operations are aqueous-based fluids that comprise gelling agents. These gelling agents may comprise biopolymers or synthetic polymers. Common gelling agents include, e.g., galactomannan gums, cellulosic polymers, and polysaccharides.
Most viscosified treatment fluids include crosslinked gelling agent molecules to increase their viscosity. The crosslinking between gelling agent molecules occurs through the action of a crosslinker. These crosslinkers may comprise a metal ion, transition metal, or metalloid, collectively referred to herein as “metal(s).” Examples include boron, aluminum, antimony, zirconium, magnesium, or titanium. Generally, the metal of a crosslinker interacts with at least two gelling agent molecules to form a crosslink between them, thereby forming a crosslinked gelling agent.
Conventional metal crosslinkers are frequently used in viscosified treatment fluids, however, use of such crosslinkers is problematic because they may not achieve a viscoelastic gel below a critical concentration of gelling agent. In addition, commonly used viscosified treatment fluids may not be thermally stable at temperatures exceeding about 200° F. such that the highly viscous gelled and crosslinked fluids lose viscosity with time at high temperatures. To offset this loss of viscosity, the concentration of the gelling agent and/or crosslinker may be increased; however, this leads to increased cost and may also make the viscosified treatment fluid more difficult to remove from the formation. It would be useful to have a crosslinked gelling agent that can be crosslinked using a reduced concentration of a gelling agent and a crosslinker. It is also desirable to crosslink the fluid at or near a neutral pH because of various problems. For instance, in some cases in which the fluid is crosslinked at a pH of 11 and above, calcium and magnesium ions may precipitate out of solution causing potential damage to the formation.